According to the 2005 Americans with Disabilities report, approximately 27 million people over the age of 15 had a walking-related disability. Ankle joint musculature plays an extremely important role during walking and is thought to be the primary muscle group that supports upright stance and produces forward propulsion. Individuals with muscular weakness about the ankle, an impairment often caused by upper motor neuron disorders and lower extremity injuries, are frequently prescribed ankle-foot orthoses (AFOs), which brace the ankle during gait and aim to improve gait function.
Passive-dynamic ankle-foot orthoses (PD-AFOs) constitute one class of ankle braces that rely on material properties and physical features to establish functional characteristics such as bending or rotational stiffness and the storage and return of mechanical energy. PD-AFOs are traditionally composed of footplate, strut and cuff components, which may be fabricated using continuous material or connected as components in various manners. Despite the great potential for biomechanical assessment and treatment using this classification of orthoses, currently prescribed PD-AFOs are often generic, having standardized size and shape (fit) and bending or rotational stiffness (functional) characteristics.
Fit customization is an important design factor for obtaining optimal function from a PD-AFO. The size and shape characteristics, which describe the fit of a PD-AFO, can be customized through a variety of methods. Traditionally, an orthotist casts a patient's shank and foot to create a negative mold. A positive mold is generated from the negative mold, and then the PD-AFO is manually fabricated around this positive mold similar to methods for fabricating a foot orthosis. While manual manufacturing methods can sufficiently generate a PD-AFO with customized size, augmented shape, and functional characteristics, manual manufacturing methods can contribute to undesirable variability in quality or effectiveness of manufactured components, depending on an orthotists' skill and experience, and may require substantial time and expertise to ultimately manufacture orthoses having functional characteristics that match the unique gait dynamics of each patient. Additionally, while this method can sufficiently generate a PD-AFO with customized size characteristics, shape characteristics such as component curvatures and joint alignment cannot be precisely tuned. Furthermore, the position of the ankle joint is fixed at the time of casting and thus clinical joint alignments cannot be made during the fabrication process. The cost of such customized devices is also substantial.
Recent efforts have worked on using computer aided design (CAD) models and associated parameterization tools to customize orthoses. At least one such parameterized orthosis model has been reported to have two rigid components, one for each of the foot and shank, attached by a single-degree-of-freedom hinge. Parameterization of this model was based on two anatomically-relevant coordinate systems, one for each of the components. Patient-specific imaging data were fit to the parameterized model to scale the orthosis. While this CAD model was parameterized for size and ankle angle, the orthosis design lacked the organic shape characteristics and parameterization of orthosis functional characteristics. Furthermore, the coordinate planes and resulting parameterization were dependent on the position of the shank and foot during collection of the imaging data.
Therefore, there is a need in the art for systems and processes that enable rapid design and manufacture of customized orthoses with precisely controlled characteristics. Such systems and processes have the potential to transform the PD-AFO customization and fabrication process from a craft-based industry into a modern clinical specialty.